1. Field of the Invention
This invention relates to a computer system connected to CSMA/CD (Carrier Sense Multiple Access/Collision Detection) LAN and capable of disconnecting itself from the LAN in case a failure takes place in the network.
2. Description of the Related Art
CSMA/CD LAN systems are generally able to transmit broadcast packets, which are addressed to all computers (devices) connected to the LAN.
Such a function, which is one of typical high-level protocols for the LAN, is essential to such as ARP (Address Resolution Protocol), ROUTED, and RWHO in TCP/IP (Transmission Control Protocol/Internet Protocol).
ARP is a protocol for calculating a MAC (media access control) address, an address on the LAN, from an Internet address (IP address), a network address (an address used to identify a device on TCP/IP) in TCP/IP. ROUTED is a program that enables the exchange of route control information between routers over a plurality of LANs. RWHO is a program that deals with information on users using the computer system.
In conventional LAN systems, however, broadcast packets sometimes develop abnormally due to mismatched settings for the network or defective programs, resulting in serious network failures.
It is known that there are two types of failures: one is called broadcast storm and the other, meltdown.
Broadcast storm is a state in which the temporary abnormal appearance of broadcast packets lowers transfer capabilities on the LAN or slows the response of the computer system to the terminals or the LAN.
Meltdown is an advanced stage of broadcast storm, or a state in which the transmission of packets develops into oscillation. Once a meltdown has occurred, there is no response from the computer system. The only way to get out of this situation is to start up all computer systems connected to the LAN.
Although the mechanism of developing such failures has been elucidated, any effective means of avoiding them has not been found yet.
As noted above, conventional CSMA/CD LAN systems using broadcast packets have the problem of permitting broadcast packets to appear abnormally, thus leading to network failures such as a broadcast storm or a meltdown.
Although how network failures including a broadcast storm and a meltdown take place has been cleared, there is no way of avoiding them. Therefore, once a network failure has occurred, each computer system connected to the network is forced to receive a large volume of meaningless broadcast packets and then to discard them. As a result of this, the computer system wastes some of its computing power on such useless jobs, degrading the processing capabilities it should have.